In known manner, the crankcase is connected to the air intake of the internal combustion engine via a separation device in order to continuously evacuate the crankcase gases and extract the suspended oil. This is what is known to the skilled person as the crankcase gas or blowby gas recycling system. Various means for separating oil from crankcase gases are used in the prior art, among which are cyclones, baffles, or similar systems with multiple changes of direction, centrifugal separators, static colaescers and dynamic coalescers. There are also impingement separator systems. In this latter family, the systems comprise a set of calibrated holes or similar acceleration openings facing an impingement (or collision) plate. The crankcase gases are accelerated when passing through the holes. The oil droplets are thus accelerated and flung against the impingement plate.
In impingement separator systems which have an impingement plate, the oil droplets flung at high speed agglomerate on the surface of the plate to form a film of oil. The speed is then reduced by an enlarged flow area and the oil film drips towards the discharge system. An alternative is to attach a coalescing or similar nonwoven felt on the impingement plate to cause coalescence of the finer oil droplets before they hit the plate. This has the effect of significantly increasing effectiveness in separating the oil mist. Impingement separators offer a better compromise between efficiency/pressure loss than cyclone separators. However, the pressure loss in these systems may be high in cases of increased gas flow rate.
Some systems also include a valve allowing a greater flow rate, sensitive to pressure, in order to partially bypass the acceleration openings made in a transfer wall (wall preceding the impingement plate). The flow rate of crankcase gases is typically higher at the end of a separators service life (for example double or triple the nominal flow for a new engine).
Solutions that allow increasing the flow rate are therefore of interest in order to limit the pressure loss at the transfer wall. For example, FIGS. 2a-2c of U.S. Pat. No. 7,799,109 show a transfer wall placed facing an impingement plate and provided with a plurality of openings for accelerating the flow of blow-by gas. A valve of flexible material is provided which is deformed to define an auxiliary opening of large cross section when a pressure threshold (overpressure) is reached upstream of the transfer wall.
This type of solution has limitations, however, notably because of the temperature sensitivity of the flexible material and because, even at low flow rates, the valves may have a slightly open state (the closure being progressive). Poor separation performance may then be observed, especially during transition phases. In addition, a closure portion of flexible material can often wear out quickly (risk of wear).
There is therefore a need for an efficient separation of oil from crankcase gases by impingement (the ultimate purpose being to improve engine durability), while taking into account flow rate variations over time.
Known from document US2013/0032115 A1 is the use of non-hermetic valves which have openings formed in the movable element (partial closure element). Regardless of the position of the valve, the gases circulate in a region behind the valve where a coil spring is placed. This type of valve has stability problems in an environment that is generally subject to vibration. In some embodiments (see FIGS. 8 and 9 of US2013/0032115 A1) it is arranged to guide the closure element in order to stabilize the valve. In this case, it is necessary to provide a complex seating of at least two parts and there is more friction between the valve and the transfer wall, which subjects this system to premature wear or makes it less effective.